MDEV-40501: Assertion `info->type == READ_CACHE || info->type == WRITE_CACHE' failed in reinit_io_cache upon CHANGE MASTER

mysql-test/suite/rpl/r/rpl_change_master_long_channel_name.result

@@ -0,0 +1,17 @@
+include/master-slave.inc
+[connection master]
+connection slave;
+CHANGE MASTER TO MASTER_DELAY=1 FOR CHANNEL '################################################';
+ERROR HY000: Could not initialize master info structure for '################################################'; more error messages can be found in the MariaDB error log
+connection master;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1);
+connection slave;
+connection slave;
+include/diff_tables.inc [master:t1, slave:t1]
+CHANGE MASTER 'new_channel' TO MASTER_HOST='127.0.0.1', MASTER_PORT=1, MASTER_USER='root';
+RESET SLAVE 'new_channel' ALL;
+connection master;
+DROP TABLE t1;
+connection slave;
+include/rpl_end.inc

mysql-test/suite/rpl/t/rpl_change_master_long_channel_name.test

@@ -0,0 +1,40 @@
+#
+# CHANGE MASTER ... FOR CHANNEL with a name that overflows the relay
+# log file name once escaped should return an error, not crash.
+#
+# STEPS:
+#   1. Issue CHANGE MASTER ... FOR CHANNEL with a channel name that is
+#      within MAX_CONNECTION_NAME, but expands past the file name
+#      limit once escaped into the relay log file name.
+#   2. Verify the statement fails with a clean error, not a crash.
+#   3. Verify the server is still usable: a normal CHANGE MASTER for a
+#      new, short-named channel succeeds.
+#
+--source include/master-slave.inc
+
+--connection slave
+--let $channel= `SELECT REPEAT('#', 48)`
+--error ER_MASTER_INFO
+eval CHANGE MASTER TO MASTER_DELAY=1 FOR CHANNEL '$channel';
+
+--connection master
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1);
+--sync_slave_with_master
+
+--connection slave
+--let $diff_tables= master:t1, slave:t1
+--source include/diff_tables.inc
+
+CHANGE MASTER 'new_channel' TO MASTER_HOST='127.0.0.1', MASTER_PORT=1, MASTER_USER='root';
+RESET SLAVE 'new_channel' ALL;
+
+--disable_query_log
+call mtr.add_suppression("Failed when trying to open logs");
+--enable_query_log
+
+--connection master
+DROP TABLE t1;
+--sync_slave_with_master
+
+--source include/rpl_end.inc

sql/log.cc

@@ -3871,15 +3871,15 @@ bool MYSQL_BIN_LOG::open_index_file(const char *index_file_name_arg,
     Create an index file that will hold all file names uses for logging.
     Add new entries to the end of it.
   */
-  myf opt= MY_UNPACK_FILENAME;
+  myf opt= MY_UNPACK_FILENAME | MY_SAFE_PATH;
   if (!index_file_name_arg)
   {
     index_file_name_arg= log_name;    // Use same basename for index file
-    opt= MY_UNPACK_FILENAME | MY_REPLACE_EXT;
+    opt= MY_UNPACK_FILENAME | MY_REPLACE_EXT | MY_SAFE_PATH;
   }
-  fn_format(index_file_name, index_file_name_arg, mysql_data_home,
-            ".index", opt);
-  if ((index_file_nr= mysql_file_open(m_key_file_log_index,
+  if (!fn_format(index_file_name, index_file_name_arg, mysql_data_home,
+                ".index", opt) ||
+      (index_file_nr= mysql_file_open(m_key_file_log_index,
                                       index_file_name,
                                       O_RDWR | O_CREAT | O_BINARY | O_CLOEXEC,
                                       MYF(MY_WME))) < 0 ||

sql/rpl_mi.cc

@@ -1483,7 +1483,8 @@ bool Master_info_index::remove_master_info(Master_info *mi, bool clear_log_files
     /* This code is only executed when change_master() failes to create a new master info */
 
     // Delete any temporary relay log files that could have been created by change_master()
-    mi->rli.relay_log.reset_logs(current_thd, 0, (rpl_gtid*) 0, 0, 0);
+    if (mi->rli.relay_log.is_open())
+      mi->rli.relay_log.reset_logs(current_thd, 0, (rpl_gtid*) 0, 0, 0);
     /* Delete master-'connection'.info */
     create_logfile_name_with_suffix(tmp_name,
                                     sizeof(tmp_name),